Installing Vista under Virtual Server 2005 R2 is significantly easier than installing under VPC or Virtual Server 2005 RTM. There are two main reasons why:
Virtual Server 2005 R2 includes the new version of the Additions that work (but are UNSUPPORTED...

Just like the topic says, this post is dedicated to getting Vista going under Virtual PC. I've divided it into two sections, just to make it a bit more readable.
Getting Vista Installed
The first issue that Virtual PC users are likely to run into...